You don't always know whats in back!
I have asked many times what we were carrying, and told, "its above your pay grade" I asked if it was animal, vegetable or mineral. Not my position to know! Wait, I'm the captain! I have a right to know! Ask the Chief Pilot????, he's ex military. Fly it , or you're fired!
It is very possible that they didn't know what it was. Sometimes it is so well packed, you couldn't possibly guess without opening it.